A variable stator vane arrangement is used to set the variable stator vanes in a compressor, or a turbine, into their desired angular position.
One known type of variable stator vane arrangement uses a crankshaft to drive a number of stages of variable stator vanes. Each stage of variable stator vanes comprises a plurality of stator vanes connected to an associated control ring by respective operating levers. The crankshaft is connected to each control ring, or unison ring, by a connecting rod. Each connecting rod is mounted onto the crankshaft by a clevis. Each clevis is provided on an associated crank arm on the crankshaft. The crankshaft is rotated around its rotational axis by a force applied by a variable stator vane actuator. The radial and angular position of the clevis on the crankshaft determines the operating schedule for that particular stage of variable stator vanes.
Conventionally all of the clevises on the crankshaft are provided in a fixed position on the crankshaft and thus the operating schedule for all the stages of variable stator vanes is fixed, e.g. each crank arm is provided at a fixed circumferential position on the crankshaft and has a fixed length. The use of fixed operating schedules for all of the stages of variable stator vanes is acceptable, and conventional, on production gas turbine engines and other turbomachines.
However, during the development programme of a gas turbine engine, or a turbomachine, it may be necessary to adjust the radial and angular positions of the clevises on the crankshaft for one or more of the stages of variable stator vanes in order to determine, or to provide, an optimum operating schedule for each of the stages of variable stator vanes. This may necessitate the manufacture of different crankshafts with clevises at different radial and angular positions and this may delay the gas turbine engine development program, increases the cost of the development programme and may compromise the results of the development programme.
Therefore the present disclosure seeks to provide a novel variable stator vane arrangement which reduces or overcomes the above mentioned problem.